This invention relates generally to rotary machines and, more particularly, to a method and an assembly for aligning an inner shell of the rotary machine with an outer shell of the rotary machine.
Steam and gas turbines are used, among other purposes, to generate power for electric generators. Known steam turbines have a steam path that typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. Known gas turbines have a gas path which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). The compressor sections and the turbine sections each includes at least one row of circumferentially spaced rotating blades or buckets.
Turbine efficiency depends at least in part on controlling a radial clearance or gap between the rotor shaft and the surrounding casing. If the clearance is too large, steam or gas flow may leak through the radial clearance, thus decreasing turbine efficiency. Alternatively, if the clearance is too small, the rotating rotor shaft may undesirably contact the stationary packing ring during certain turbine operating conditions, thus adversely affecting turbine efficiency. Gas or steam leakage through the packing assembly represents a loss of efficiency and is generally undesirable.
To minimize leakage and prevent undesirable contact between rotating components and stationary components, the inner shell of the turbine is keyed axially and transversely to the outer shell of the turbine along the respective axial centerline and transverse centerline. Gib keys are generally positioned between the inner shell and the outer shell to properly align the inner shell with the outer shell during turbine assembly. Conventional gib keys typically have a generally circular disc shape and are fastened to the inner shell with a bolt. The dimensions of the packing head positioned within the inner shell, particularly a length of the packing head along the axial centerline, are limited by the circular disc shape of the conventional gib key. As a result of the dimensional limitations on the packing head, a sufficient number of packing rings are not positionable within the packing head to prevent or limit undesirable leakage, which negatively impacts turbine performance and efficiency.